High speed apparatus for forming foam cushions for packaging purposes

ABSTRACT

A sealing and severing apparatus is disclosed for sealing plastic bags formed in succession from stock plastic film material and then severing the sealed bags from one another. The bags are filled with a foamable composition while they are being formed so that when the formed and filled bags are placed in a container, the foamable composition fills the bag with foam to thereby produce a customized foam cushion for any objects in the container.

This application is a continuation of application Ser. No. 08/345,988,filed Nov. 28, 1994, now abandoned which is a divisional of applicationSer. No. 07/766,810, filed Sep. 26, 1991, now U.S. Pat. No. 5,376,219.

FIELD OF THE INVENTION

The present invention relates to methods for forming and filling plasticbags with foam for packaging purposes, and in particular relates to ahigh speed, just-in-time apparatus for such purposes.

BACKGROUND OF THE INVENTION

This invention is an apparatus for forming foam cushions for packagingpurposes. It is related to the apparatus and methods described in U.S.Pat. Nos. 4,800,708, and 4,854,109, both assigned to the assignee of thepresent application. These patents are incorporated entirely herein byreference. As set forth in these patents, such apparatus are used toautomatically fabricate foam filled bags. The foam is initially added tothe bag as a foamable composition or as foam precursors, typicallypolymeric compositions, and after which the bag is placed in a containerwith an object to be protected by the foam. The nature of the foamablecomposition causes it to generate gases such as carbon dioxide and watervapor which form bubbles in the polymer to create the foam as thepolymer hardens or sets. The apparatus described in the '708 and '109patents have met with a great deal of success in the marketplace, andaccordingly they have been subject to further study and improvementswhich are the focus of the present invention. In particular, the presentinvention has been addressed at increasing the speed of operation andthe simplicity of operating and maintaining the apparatus.

The present invention provides a flexible and complete foam-in-placeprotective packaging system which is extremely sophisticated infunctions and flexibility, but simple to operate and maintain. Thesystem can work in numerous configurations including a stand aloneconfiguration or in conjunction with a conveyor. It will be understoodthat the invention can be operated independently with its own chemicalsupply, or it can be included with a number of other units sharing bulkchemical supplies located in remote locations. The present invention canalso be integrated in a line with box forming and closure systems toprovide a complete packaging system. The present invention can createfoam filled bags of varying lengths and fill percentages, in"just-in-time" fashion, for a wide variety of protective packagingapplications.

OBJECT AND SUMMARY OF THE INVENTION

In one aspect, the invention can be viewed as a sealing and severingapparatus for successively forming, filling and sealing plastic bagsfrom stock plastic film material and then severing the bags from oneanother. In this aspect, the apparatus comprises a crosscut wire forsevering plastic film in contact with the wire when the wire is heatedto an appropriate temperature, means for heating the wire, and means forbringing the plastic film material from which the bags are formed intocontact with the wire.

In another aspect, the invention can be viewed as a sophisticatedsealing roller system for sealing plastic film material that is inmoving contact with the sealing roller.

In yet another aspect, the invention can be considered to be a feedingsystem for feeding a web of plastic film material from a supply roll ata desired tension regardless of the supply of film material on thesupply roll, and of controlling the tension on a web of plastic filmmaterial fed from a rotating supply roll.

In another aspect, the invention comprises a method of substantiallymatching the tension applied to two opposing webs of film material thatare being brought together to be sealed and formed into bags.

The foregoing and other objects, advantages and features of theinvention, and the manner in which the same are accomplished, will bemore readily apparent upon consideration of the following detaileddescription of the invention taken in conjunction with the accompanyingdrawings, which illustrate preferred and exemplary embodiments, andwherein:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall perspective view of the invention in its housingand on its frame support;

FIG. 2 illustrates a bag of the type formed by the present invention;

FIG. 3 is a cross-sectional view of the roll feeding, side sealing andcrosscut portions of the present inventions;

FIG. 4 is a cross-sectional view similar to FIG. 3 but showing a furtherstep in the process;

FIG. 5 is an exploded view of a number of the key features of theinvention, particularly the film feeding and sealing and crosscuttingaspects;

FIG. 6 is a partially exploded perspective view of the side edge sealingportion of the invention;

FIG. 7 is a cross-sectional view taken along lines 7--7 of FIG. 6;

FIG. 8 is a partially exploded perspective view of the electricalcontact portion of the side seal assembly of FIG. 6;

FIG. 9 is a partial perspective view of a portion of the side edge sealapparatus in relationship to the other portions of the apparatus;

FIG. 10 is an enlarged view of a portion of FIG. 9 as indicated therein;

FIG. 11 is a perspective view of the film supply, edge sealing andcrosscut portions of the invention;

FIG. 12 is an illustration of the wrist control system according to thepresent invention; and

FIG. 13 is a side elevational view of the side seal assemby of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an overall perspective view of the entire apparatus which isgenerally designated at 20. The apparatus includes a support frameassembly 21, portions of which are shown as the legs and rollers inFIG. 1. The support frame is covered by a series of removable panelswhich are designated as 22, 23, and 24 in FIG. 1. Reference numeral 22indicates those portions of the removable panels that cover the uprightportions of the support frame, and reference numerals 23 and 24designate the cover portions for the plastic film feed, fill and sealportions of the apparatus. FIG. 1 also shows an operator control panelassembly 25 and the main power switch 26. FIG. 1 additionallyillustrates a pair of hoses 27 that supply the foam-in-place chemicals,usually supplied in two components that are mixed just as they areplaced in the bag. These components are fed from a supply system which,as explained earlier, can either be an individual stock supply for onedevice, or a bulk supply for several such devices. The hoses lead to aninjection cartridge that is not shown in FIG. 1, but rather ispositioned behind one of the rolls of plastic sheet material in the viewaccording to FIG. 1.

FIG. 2 illustrates a bag of the type generally formed by the apparatus20. The bag is designated broadly at 30 and comprises a top seal 31 abottom seal 32, respective side seals 33 and 34, and respective ventopenings 35 and 36. The openings 35 and 36 permit the gases generated bythe foam precursors to exit the bag 30. In the absence of theseopenings, the gas pressure would generally rupture the bag and thusdestroy its usefulness, and perhaps damage the very items it wasintended to protect.

THE CROSSCUT SEVERING AND SEALING SYSTEM

FIGS. 3 and 4 illustrate a number of the crosscut sealing and severingfeatures of the invention in somewhat more detail.

These figures illustrate respective supply rolls of plastic filmmaterial 37 and 40. As illustrated therein, the supply rolls 37 and 40forward respective sheets 41 and 42 of plastic film material into thedevice. As a first point of explanation, the invention comprises asealing and severing apparatus for sealing plastic bags formed insuccession from stock plastic film material and then severing the sealedbags from one another. Thus the invention comprises a crosscut wire 43which when heated first seals the plastic film material 41 and 42together, and then severs it so as to concurrently form the bottom ofone bag and the top of the next while separating those bags from oneanother. The crosscut wire 43 is appropriately connected to means forheating the wire to a temperature that will sever plastic film material,typically a source of electric current, in which case the wire 43 isformed of nichrome or another suitable metal or alloy.

As used herein, the term "sealing" wire is used interchangeably with thephrase "crosscut" wire to designate that the wire 43 makes the top andbottom or "crosscut" seals in the advancing plastic film and theresulting bags.

With regard to the description of FIGS. 3 and 4, it will be understoodthat many of the same features are illustrated in FIG. 5 in explodedfashion.

An actuator bar 44 is positioned parallel to the wire 43. The actuatorbar 44 is preferably formed of a flexible material as it has been foundthat in working with foam-in-place bags and the related machinery, thepresence of hardened foam can cause problems in operating such devices.In particular, hardened foam tends to interfere with overly ridgedelements that have closely defined movements. Because of the nature ofcommonly used foamable compositions, i.e. separate liquids that generategases while solidifying into foam, excess hardened foam is almost alwayspresent in and around the apparatus. Stated somewhat differently,because the actuator bar 44 is flexible, excess foam on the exterior ofa bag or otherwise present in its vicinity that it encounters will notprevent the actuator bar 44 from operating in the manner describedherein.

Additionally, the flexibility of the actuator bar 44 helps exert anequal force across the entire sealing area.

A sealing roller 45 is also positioned parallel to the wire 43 and tothe actuator bar 44, and is on the opposite side of the wire 43 from thebar 44. The sealing roller 45 is preferably similarly formed from aflexible material, and for the same reasons as the actuator bar 44. Adriver shown as the solenoid 46 is operatively connected to the actuatorbar 44 for driving the bar 44 against the wire 43 and then the wire 43against the sealing roller 45 to thereby seal and sever plastic filmmaterial 41 and 42 passing between the sealing wire 43 and the sealingroller 45. Because the sealing roller 45 can rotate, it tends to presenta slightly different portion of itself during repeated sealing cycles,even though its rotation is not specifically driven. Additionally, if anoperator decides that the roller should be turned, they can do so easilyby hand.

In preferred embodiments, the driver is a two coil solenoid for activelydriving the actuator bar 44 in opposite directions as desired. Thenature of the force exerted by a solenoid is also such that the force ismaximized when the solenoid is most fully extended, and minimizedotherwise, so that if an operator should by accident place their hand inoverly close proximity to the actuator bar 44 and the roller 45, theforce exerted if the hand were struck or caught between parts isminimized and would thus minimize or eliminate injury to the operator.

Further to this safety feature, the heating means for the wire furthercomprises means for preventing the wire from heating until the actuatorbar is in contact with the flexible sealing roller. This is accomplishedelectronically by use of a "smart switch" that prevents the wire frombeing heated until the actuator bar is in contact with the flexiblesealing roller.

As part of the operation of the sealing wire 43 and the associated partsjust described, there is, of course, means for feeding plastic filmmaterial between the wire and the flexible sealing roller, and thesewill be described in more detail further herein.

In a preferred embodiment, the crosscut sealing wire 43 furthercomprises a respective spring at opposite ends thereof for mounting thecrosscut wire against the tension of the spring, and means on theapparatus for receiving the springs so that the sealing wire can bepositioned and maintained in position in the absence of otherattachment. This is perhaps best illustrated in FIG. 5 in which the wire43 is shown connected to respective handles 47. The handles can fit intothe respective mounting plates 50 and 51 by being placed in therespective openings 52 and 53. The spring portions of wire 43, which aregenerally too small to be clearly illustrated in the scale of FIG. 5,are positioned at either terminal end of the wire 43 immediatelyadjacent to handles 47.

The spring portions of the wire 43 also permit it to remainappropriately taut and in place during thermal expansion and contractionas an appropriate heating current is applied through it.

Additionally, in preferred embodiments the terminal portions of thecrosscut wire include means for reducing the electrical resistancethrough the terminal portions. By reducing the resistance, theseportions--which often do not come in contact with plastic film to besealed--remain cooler and avoid wasting electrical and thermal energy.In one preferred embodiment the wire 43 is double wrapped at theterminal portions thereof for reducing undesired heat dissipation fromthe wire, but the reduction in resistance could similarly beaccomplished by other conventional means.

In the preferred embodiment, the sealing and severing apparatus furthercomprises means for maintaining the crosscut sealing wire at an idlingtemperature that is above ambient temperature but below the temperatureat with sealing takes place to thereby provide for more rapidly raisingsaid sealing wire to the sealing and severing temperature wheneverdesired.

In a preferred embodiment, the means for maintaining the crosscut wireat the idling temperature comprises means for applying an idling voltageto the wire that keeps it at an elevated temperature, but a temperaturethat is below that at which the plastic film material would becomesevered. Thus, in order to raise the temperature to severing ortemperature, an additional voltage is applied which quickly raises thetemperature. This ability to rapidly raise the temperature is one of thefeatures which greatly increases the speed of the overall device.

Perhaps just as importantly, because the wire 43 is kept in a preheatedcondition, its temperature changes less drastically when it is raised tosealing temperature. The less drastic temperature excursion reduces thephysical expansion and contraction of the wire 43 and thus moderatesfatigue and increases the usable lifetime of the wire.

THE EDGE SEALING SYSTEM

As another feature which increases the overall speed of the apparatus,the invention comprises an improved system for sealing plastic filmmaterial that it is in moving contact with a sealing roller. Asillustrated by FIG. 2, and as set forth in clear detail in the '109 and'708 patents, one of the main steps in formation of a foam filled bag issealing the side portions to form the two side edges of the bag. In therespective devices described in the '109 and '708 patents, this was doneby bringing a heated metal roller into contact with the advancingplastic film material so that the heated metal formed the side seals asthe plastic film advanced. Because heated metal rollers where used,however, they had to be mechanically moved into, and then out of,contact with the advancing film material to form the seal, to leave anunsealed portion to act as the vent opening 36, or to keep the device inan idling mode if the next bag was not immediately needed.

The sealing roller system of the present invention improves on thistremendously by using a rotatable cylinder illustrated in the drawingsat 54. The rotatable cylinder 54 is formed of a thermally conductivepolymer material for dissipating heat quickly therefrom. Suitablepolymer materials include the VESPEL® polyimide materials available fromDuPont.

A sealing wire 55 is wrapped around the circumference of the polymercylinder 54. The sealing wire 55 is illustrated in exploded fashion withrespect to the rotatable cylinder 54 in FIG. 5 and schematicallyillustrated as surrounding the cylinder 54 in FIGS. 3 and 4.

As further illustrated in the cross sectional view of FIG. 7, the wire55 fits in a slight groove 56 in the circumference of the rotatablecylinder 54 and receives the sealing wire 55 therein.

FIGS. 6, 9, 10, and 13 illustrate further features of the sealing rollersystem. FIGS. 9 and 10 illustrate that a spring 57 is at either end ofthe sealing wire 55 and applies a bias to the wire that maintains it inthe groove 56 during expansion and contraction of the wire as itstemperature increases and decreases. In this regard, the sealing rollersystem includes means for raising the temperature of the sealing wire toa heated temperature that will seal plastic film material so that whenplastic film material such as 41 and 42 passes against the cylinder 54,the heated wire 55 seals the plastic film material. Generally speaking,the means used to raise the temperature comprises a source of electriccurrent that can be supplied to the wire 55 in otherwise conventionalfashion.

Because the spring 57 is larger in diameter than the wire 55, a springreceiving recess 60 is provided in the cylinder 54 for keeping thespring 57 out of contact with the plastic film 41 and 42 during edgesealing. A pair of respective pins 61 are present in the respectiverecesses 60 for attaching the springs 57 thereto so that the bias of thesprings 57 helps maintain the wire 55 in the groove 56 and on thecylinder 54. FIG. 13 illustrates that each cylinder 54 has a pair ofcorresponding pins 61 and recesses 60.

In preferred embodiments, the cylinder 54 includes a pair of electricalcontacts 59 (FIG. 13) across which the wire passes so that a voltageapplied to the contacts 59 will be correspondingly applied to the wire55 to heat the wire 55 as the applied voltage generates a currenttherethrough. In this regard, the springs 57 help maintain goodelectrical contact by urging the wire 55 against the contacts 59.

In the most preferred embodiment, this system further comprises meansfor maintaining an idling voltage in the sealing wire 55 that maintainsthe wire 55 at a temperature below the temperature at which the wire 55will seal the plastic film material 41 and 42, but which allows the wire55 to more quickly reach such a sealing temperature upon desiredcommand. The use of an idling voltage also reduces temperatureexcursions and metal fatigue in essentially the same manner as does theuse of the idling voltage with the crosscut wire 43.

As further indicated by the drawings, particularly FIG. 13, the wire 55is preferably wrapped around the cylinder 54 in a slight spiral patternin a direction which prevents foam from escaping from the bag as it isbeing formed.

The purpose of providing the cylinder 54 from a thermally conductivematerial is to provide for rapid dissipation of heat from the wire. Inother words, in the prior devices such as described in the '109 and '708patents, the necessary vent openings 35 and 36 in the bag 30 were formedby physically moving the side edge rollers out of contact with theplastic material for a short period of time to thus leave the unsealedportion. This mechanical movement required a finite amount of time,however, which in turn reduced the speed with which any individual bagcould be formed, and thus reduced the device's overall rate of bagformation.

The invention addresses this problem with the combination of the wire 55and the thermally conductive cylinder 54. Because the cylinder 54 isthermally conductive, and because the sealing is done by a wire 55rather than a metal roller as in previous versions, the openings 35 and36 are formed in the bag by simply turning off the current to the wire55 for a short period of time so that the wire 55 is no longer heated tothe temperature at which it will seal plastic. In order to successfullyaccomplish this, however, heat must be carried away from the wire 55very quickly so as to insure that the unsealed portions for the openings35 and 36 are not undesirably sealed by residual heat in the wire. Thus,the provision of a thermally conductive polymer material for therotatable cylinder 54 draws heat away from the wire 55 rapidly once thevoltage applied to the wire is dropped. In this manner, the rotatablecylinder 54 and the sealing wire 55 can be maintained in constantcontact with the plastic film material 41 and 42, while the ventopenings 35 and 36 can be produced on command. Because this eliminatesmuch of the mechanical motion in the prior devices, it greatly increasesthe speed with which the invention can produce foam-in-place bags.

In one embodiment of the invention which is not otherwise illustrated,the plastic sheet material, rather than being fed from two rolls asillustrated, is fed from a single roll of sheet material which is foldedsubstantially in half to form one side edge of the resulting bag. Itwill be understood that in forming a bag from such stock material, theside edge sealing and top and bottom sealing will be identical to thatdescribed herein, with the sole exception being that instead of two sideseals being formed, only one will be required. It will be understoodthat a device which uses folded plastic in such a manner is entirelywithin the description and claims of the present invention, andotherwise does not represent any departure from this specification, orthe appended claims.

In the preferred embodiment, the invention comprises a pair of therotatable polymeric cylinders 54 mounted on a rotatable shaft 62 (FIG. 5and FIG. 6). In order to advance the plastic, a pair of drive rollers 63are likewise mounted on a second rotatable shaft 64 which is parallel tothe first rotatable shaft 62. The drive roller 63 are respectivelypositioned opposite to the polymeric cylinders 54, and the first andsecond shafts 62 and 64 respectively are positioned sufficiently closelyfor rotation of the drive rollers 63 to drive the rotation of thepolymeric cylinders 54 independently of the presence or absence ofplastic film material 41 and 42 between the drive roller 63 and thepolymeric cylinders 54. The drawings further illustrate that the shaft62, in order to be appropriately driven by the drive roller 63, includessome additional followers 65 which provide extra surface area to engagethe drive roller 63 and to rotate the cylinders 54.

As perhaps best illustrated in FIG. 5, for convenience and simplicity ofassembly, mounting, and disassembly, the drive rollers 63 are mounted onshaft 64 using keyhole openings 66 which match the shaft 64 andcorresponding pins 67 in the shaft. FIG. 5 also illustrates that theshaft 62 and the other elements that it carries are mounted on theplates 50 and 51 in the openings 70 and 71 respectively therein usingthe hub portions 72 on either end of the shaft 62. Similarly, the shaft64 is mounted on plates 50 and 51 in openings 73 and 74 respectivelyusing the hub portion 75 on the shaft 64.

In this regard, it will be understood that there are a number offasteners and the like between the respective parts that could beillustrated and described with respect to FIG. 5 but which are otherwiseconventional, and thus have not been illustrated for the sake of overallclarity of the drawing and for the further sake of more clearlyillustrating other features of the invention.

In a preferred embodiment, the drive rollers 63 are formed of a siliconerubber compound such as those available from General Electric under the"RTV" trademarks. As another detail of the preferred embodiment, when apair of rotatable cylinders 54 are used, the pins 61 and the grooves 60in one cylinder 54 is rotationally offset with respect to the othercylinder 54. This provides an additional measure of assurance that thebag will be sealed properly when formed.

As further illustrated in FIGS. 3, 4, and 5, a pair of film guides 76and 77 are positioned above the first and second shafts 62 and 64 forreceiving the plastic film 41 and 42 therebetween so that the plasticfilm is more efficiently presented to the drive rollers 63 and thepolymeric cylinders 54. In the preferred embodiment, the film guides 76and 77 comprise adjacent bars parallel to the first and second shafts 62and 64 and positioned laterally away from the position at which thedrive rolls 63 and polymeric cylinders 54 meet in a direction toward thedrive rolls 63. This positioning encourages the plastic film material 41and 42 to meet the drive rolls 63 prior to meeting the polymericcylinders 54, and to thereby be more effectively advanced through theapparatus. This positioning also keeps the plastic film material awayfrom the side edge rollers until the plastic as at the desired sealinglocation.

In the more preferred embodiments, the film guide bars further comprisea plurality of downwardly depending guide canes 80 and 81 which hangfrom the guides 76 and 77 for further directing and advancing theplastic film 41 and 42 between the drive rolls 63 and the polymericcylinder 54 and for preventing the plastic film 41 and 42 from wrappingaround either of the shafts 62 or 64 as the film 41 and 42 advancesdownwardly. For the sake of clarity, the canes 80 and 81 have beenillustrated in FIGS. 3 and 4 as ending just above the drive rollers 63.In preferred embodiments, however, the canes 80 and 81 are somewhatlonger and can extend almost as far downwardly as the solenoid 46. Toaccomodate this length, the drive rollers 63 have circumferentialgrooves 68 therein (FIG. 5) so that the guide canes will not intereferewith the dirve rollers or vice versa.

In the most preferred embodiment's, at least some of the guide caneshave flexible lower portions for preventing advancing plastic film fromtearing whenever it engages the guide canes. In the figures, theseflexible lower portions are shown as the small springs 82 on the guidecanes 81 that are on the sealing roller side of the plastic film. Giventhe slight offset position of the guide bars 76 and 77 illustrated inFIGS. 3 and 4, it has been determined that the flexible lower portionsare most useful in this position, as the plastic film material wouldotherwise be more likely to tear against guide cane 81 then againstguide cane 80.

As perhaps best illustrated in FIG. 8 the first shaft 62 also has aplurality of electrical contact rings 83 on the hub portion 72 thereof.These rings 83 are in respective electrical contact with the contact 59and the wires 55 for making electrical contact with the source ofelectricity, illustrated as the connector 84 in FIG. 8, and forproviding a path for electrical current to flow from the source to thewires to thereby heat the wires to the temperatures required to eitheridle the wire or seal the plastic film material.

THE PLASTIC FILM FEEDING SYSTEM

The feeding system of the present invention comprises a rotatable shaft,two of which are illustrated in the drawings, and which are broadlydesignated at 85, and first portions of which are designated at 88. Therotatable shafts 85 carry the respective supply rolls 37, 40 of plasticfilm material. A motor 86 is connected to each shaft 85 for retardingthe rotation of the shaft. Means are included for measuring theelectromotive force (EMF) generated by the rotation of the shaftwhenever the motor 86 is inoperative, as explained more fully herein,and means are included for controlling the force applied by the motor 86in response to the generated EMF to thereby apply a desired amount oftension to the web of film material.

In this regard, it has been determined by use of previous apparatus,such as those described in the '109 and '708 patents, that when therolls of 37 and 40 of plastic film material differ somewhat in size, thelever arm formed by the plastic film between the supply roll and thedrive rolls correspondingly differs in length. As a result, themechanical tension applied to each web of film by the driving force ofthe rollers 63 will differ, thereby causing certain problems in theadvancement and production of film material and bags. As might beexpected, the ideal situation is when both rolls are of the same sizeand thus equal tension is inherently applied. Such is generally not thecase, however, in actual circumstances. Therefore, the invention hasbeen developed and improved to provide equal tension, regardless ofdifferences in roll sizes.

Thus, in preferred embodiments, the motors 86 comprise direct currentmotors. These are electrically connected to an electronic control, andto voltage and current sources so that a braking voltage can be appliedto the direct current motor 86 to retard the rotation of the shaftportions 88 and in turn retard the feeding of plastic film. In otherwords, as illustrated by the arrows at the top of FIG. 3, the left handroll 37 rotates in a clockwise direction as it advances plastic filmmaterial 41, and the right hand roll 40 advances in a counterclockwisedirection as it advances the plastic film 42. Thus, the motor 86 thatcorresponds to supply roll 37 will have the capacity to drive the roll37 in a counterclockwise direction, and likewise the motor 86 associatedwith supply roll 40 will have the capacity to drive roll 40 in clockwisedirection.

The motors are used in a method of controlling the tension on the web ofplastic film material fed from the rotating supply rolls 37 and 40. Themethod comprises measuring the EMF generated by the motor 86 attached torotate with the supply roll (37 or 40) Of plastic film material, andthen driving the motor 86 in a direction opposite to the supply rotationwith a force sufficient to provide a desired tension to the web 41 or 42of plastic film material. In a preferred embodiment, this methodcomprises measuring the EMF generated by the motor at periodic intervalscorresponding to periodic advancement of the web of plastic filmmaterial--i.e. the formation of one bag--and then driving the motor inthe opposite direction on a periodic basis corresponding to the periodicmeasurement of EMF. In particular, the method comprises comparingmeasured EMF from the motor to a predetermined standard to determinewhether the corresponding web tension is acceptable prior to the step ofdriving the motor in the opposite direction.

Stated somewhat differently, when the plastic film materials 41 and 42are advancing in the fashion illustrated in FIGS. 3 and 4 in a mannerwhich forms a bag, the motors 86 are periodically turned off for a briefperiod, for example about 50 milliseconds (i.e. 0.050 seconds; a bagtakes approximately 2 seconds to make). During this brief period, themotors 86 do not apply any force, but are treated as generators so thatan EMF is produced by the rotation of the motor as they follow therotation of the respective supply rolls. In a manner well known to thoseof ordinary skill with respect to direct current motors, this EMF is ameasure of the speed of rotation of the shaft 85 and is thus a measureof the tension applied to the plastic film material 41 and 42. Theelectronic controls of the present invention measure this "back EMF" anduse it to compute the tension applied to the individual webs 41 and 42.If the respective tensions applied to the webs 41 and 42 are different,or for any other desired reason, the motors 86 are then driven in theopposite direction for very brief periods of time to thereby drive theshafts 85 in respective opposite directions for that period of time, andthus apply the appropriate tension to the plastic film.

Thus, when two shafts are used the method can be understood as the stepof advancing two opposing webs of plastic film material in periodicincrements from the respective supply rolls and into face-to-facerelationship, measuring the EMF generated by a respective motor attachedto rotate with each supply roll of plastic film material, and thendriving each respective motor in a direction opposite to the supplyrotation of its supply roll, and at a force sufficient to provide adesired tension to each web being fed from each respective supply roll.In the most preferred embodiment, the motors will be driven to produceequal tensions.

As illustrated in FIG. 5, the film feeding system includes terminalportions 87 on the shafts 85 which are formed of a flexible material sothat if an excess force is applied to these portions 87, they will flex,rather than break or otherwise damage the machine. This is particularlyuseful when full supply rolls such as 37 and 40 are being added to theapparatus as illustrated in FIG. 11.

Other details of the shaft 85 include a plurality of flexible bowsprings 90 which help maintain the hub of a supply roll 37 or 40 on theshaft 85.

Additionally, a sensing ring 91 is positioned on the shaft 85 next to athrust bearing 92 adjacent one edge of the supply roll such as 37 or 40for changing position toward the supply roll when the diameter of thesupply roll of plastic film material becomes smaller than the diameterof the sensing ring. In this manner, the ring 91 indicates that thesupply of plastic film material has been reduced below a predeterminedamount. In other words, as long as the supply of film material on supplyroll 37 or 40 is sufficient to keep the diameter of the supply rolllarger than the diameter of the sensing ring 91, the sensing ring 91will be maintained at a terminal portion of the shaft 85 adjacent themotor 86 (FIG. 5 is an exploded view, and the sensing ring 91 is in usepositioned adjacent the motor such as illustrated in FIG. 11). When thesupply roll 37 or 40 becomes small enough, the diameter of the roll willbecome smaller than the sensing ring 91, at which point the rotation ofthe respective supply roll 37 or 40 tends to cause the sensing ring 91to move over the supply roll to alert the operator to the reduced amountof plastic film. It has been found according to the present inventionthat the ordinary movement of the film is enough to cause the sensingring 91 to move in this manner so that other bias is unnecessary and canbe omitted if desired.

Some further details of the invention are illustrated in the drawings.FIG. 5, for example, also illustrates a motor 93 which drives the driveroll 63 on shaft 64. FIG. 5 additionally shows an encoder 94 for thedrive system to provide feedback on the edge seal process.

FIG. 5 further illustrates a mounting bracket 95 which holds theinjection nozzle that dispenses the foam precursor (not shown). Forexplanatory purposes, a small portion of such a nozzle is illustrated at96 in FIGS. 3 and 4.

With respect to the actuator bar described earlier, FIG. 5 illustratesthat the actuator bar includes a small male mounting bracket 97 whichcorresponds to a female seating bracket 100 on a stationary member bob.As described earlier, the actuator bar 44 is driven by the solenoid 46and the relationship between the male mounting 97 and the female seat100 is such that the actuator bar 44 is returned to a proper positioneach time it cycles through a sealing operation.

FIG. 5 also illustrates that in order to help secure supply rolls suchas 37 and 40 on the shaft 85, the shaft includes a gripping systemformed by the handle 103 and the wedge member 104. Although illustratedin exploded fashion in FIG. 5, the wedge member 104 is fixed on theshaft portion 88. A set of radially extendable pins 105 on the wedgemember 104 are controlled--i.e. extended outwardly--by turning thehandle 103. The extended pins 105 apply an appropriate gripping force tothe interior hub of the supply roll, and thus help hold it in place.

FIG. 6 illustrates that with respect to the electrical connectionsformed by the electrical contact rings 83, a plurality of wires 102carry current appropriately to the contacts 59 and wires 55 previouslydescribed with respect to the side seal mechanism.

Finally, FIG. 12 illustrates a particularly useful feature of thepresent invention, namely the use of a wrist mountable controllerbroadly designated at 105. The wrist controller 105 includes a controlpanel 106 with the appropriate buttons for controlling the length ofbags produced, and the percentage of filling desired in each bag. Thewrist controller 105 sends a signal to the main controller of the devicethrough an appropriate electromagnetic signal such as a radio frequency("RF") signal (preferably at 303.875 megahertz, MHz), that permits theoperator of the machine to run it while standing some distance away fromthe actual control panel 25. In other words, if the apparatus 20 wasused along an assembly or packaging line, the operator could standupstream or downstream from the apparatus performing an additional taskwhile commanding the apparatus to produce a foam-in-place bag asnecessary when a container passed beneath it.

SEQUENCE OF EVENTS

A typical sequence of events thus begins when the operator pushes a foamamount button and a bag length button on the wrist control unit 105. Ifall conditions are satisfactory, the apparatus will feed film, dispensechemicals, and cut and seal a bag. The wrist control unit sends a signalto the console 25 to open the cartridge and dispense chemical for apreset length of time. Next, the film feed motor is activated. While thefilm is being fed, the edges of both sheets of film are welded togetherby the edge seal drive assembly as described herein. An idle voltage iskept on the edge seal wire while the machine is at rest and is increasedto a full voltage as the bag is made. The vent hole is made on either orboth sides of the bag near the top to allow for off-gassing of therising foam. As described herein, the vent is made by turning thevoltage off for a very brief period of time, typically 150 milliseconds.

Prior to the cartridge closing, the solvent pump and pumping systemwhich is the subject of co-pending application Ser. No. 07/767,033, toSperry et al. for "Improved Pumping and Cleaning System For Foam InPlace Injection Cartridges," and filed concurrently herewith, now U.S.Pat. No. 5,255,847, activates for a cleaning cycle, typically offorty-five seconds. This time period is reset each time the cartridgeopens and closes. The solvent used for cleaning the cartridge is held ina container mounted in a rack in the lower right side of the frame 21,but which is not otherwise illustrated herein. There is a solvent pumpinside the solvent container as described in co-pending application Ser.No. 07/767,033, now U.S. Pat. No. 5,255,847 which delivers the solventto the tip of the cartridge. The air pump mounted on the frame in anyconvenient location delivers air to the cartridge tip. The net effect isto combine a flow of solvent and the air to produce a frothing action onthe tip of the cartridge which washes off the liquid foam. The generalcleaning principle is also set forth in U.S. Pat. No. 4,898,327, whichis also assigned to the assignee of the present invention.

Next, the actuator bar is pulled back into the female stop bracket bythe solenoid to properly align it with the crosscut roller. At the sametime the edge seal is being completed after the vent has been formed.The actuator bar is pushed forward by the solenoid into the foam filledbag. The crosscut wire sits at rest with an idle voltage. As the machinefinishes feeding the bag, the crosscut wire goes to full voltage, thesolenoid goes to the home position, and the film drive motor reversesdirection to break the film apart. In a preferred embodiment a beep willsound a signal that the cycle is complete.

The device can be used in conjunction with any appropriate deliverysystem for foamable compositions or their precursors, such as theInstapack 808 dispenser system available from Sealed Air Corporation,Danbury, Conn.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms havebeen employed, they have been used in a generic and descriptive senseonly and not for purposes of limitation, the scope of the inventionbeing set forth in the following claims.

That which is claimed is:
 1. A sealing and severing apparatus forsealing plastic bags formed in succession from stock plastic filmmaterial and then severing the sealed bags from one another, saidapparatus comprising:a crosscut wire for severing plastic in contactwith said wire when said wire is heated to a temperature that will sealand sever plastic; means for heating said wire to a temperature thatwill sever plastic film material; a sealing actuator bar parallel tosaid wire; a sealing roller parallel to said wire and said bar, and onthe opposite side of said wire from said bar; means for feeding plasticfilm material between said wire and said sealing roller and comprising,afirst rotatable shaft having a pair of driven cylinders mounted thereon;a second rotatable shaft parallel to said first rotatable shaft; a pairof drive rollers on said second shaft and positioned respectivelyopposite to said driven cylinders; and wherein said first and secondshafts are positioned sufficiently closely for rotation of said driverollers to drive the rotation of said driven cylinders independently ofthe presence or absence of plastic film material between said driverollers and said driven cylinders; a pair of adjacent film guide barsabove said first and second shafts for receiving a plastic filmtherebetween, said bars being parallel to said first and second shaftsand positioned laterally away from the position at which the driverollers and driven cylinders meet in a direction toward the driverollers to thereby encourage the plastic film material to meet the driverollers prior to meeting the driven cylinders and to thereby moreeffectively present the plastic film to said drive rollers and saiddriven cylinders; and a driver in operative connection to said actuatorbar for driving said bar against said wire and said wire against saidsealing roller to thereby seal and sever plastic film material passingbetween said sealing wire and said sealing roller.
 2. A sealing andsevering apparatus according to claim 1 wherein said film guide barsfurther comprise a plurality of downwardly depending guide canes forfurther directing an advancing plastic film between said drive rolls andsaid driven cylinders, and for preventing plastic film from wrappingaround either of said shafts as it advances downwardly.
 3. A sealing andsevering apparatus according to claim 2 wherein at least some of saidguide canes have flexible lower portions for preventing advancingplastic film from tearing whenever it engages said flexible lowerportions.
 4. A sealing and severing apparatus according to claim 1wherein said driven cylinders each include a circumferential sealingwire and said first shaft has a plurality of electrical contact rings onone terminal end thereof for making electrical contact with a source ofelectricity and for providing a path for electrical current to flow froma source to said circumferential sealing wires to thereby heat saidcircumferential sealing wires to the temperature required to sealplastic film material.